Various types of earthquake sensors are known in the patent literature. The following U.S. Patents are believed to represent the state of the art: U.S. Pat. Nos. 4,086,807; 4,262,289; 4,297,690; 4,358,757; 4,484,186; 4,662,225; 4,689,997; 4,764,761; 4,764,762; 4,789,922; 4,841,288; 4,904,943; 4,945,347; 4,978,948; 4,980,644; 5,001,466; 5,101,195; 5,248,959; 5,278,540.